Backlinks and search engines

Backlinks, also named inbound links, reflects the popularity of a site and its audience. For webmasters, they are the key factor in search engine optimization, for improving the traffic of a site.

They give visibility to an article on the Web and provide visitors who follow links, but also improve the score of the article (PageRank) to the algorithm of search engines, and thus its ranking in results and thus, its traffic. It is important to know why webmasters add these external links and where they do not add them.

Matt Cutts was the member of the Google's SEO staff who communicates the most often on medias about the algorithm. He said in an interview published on the Stonetemple site, in Octobre 8, 2007:

"I would certainly say that the links are the primary way that we look at things now in terms of reputation."

Summary:

When links are added to documents

External links are added in a document in the following cases:

These links may be added in different parts of a web page of various media:

Who is likely to get backlinks

What are the conditions for a site to get backlinks?

The rules are different for blogs. The social networking aspect outweighs the other, one must have friendly sites to have links.

There is little chance of getting back links in the following cases:

Some advice to how to get backlinks.

Importance of design

Various aspects in the design of a site should be considered for getting backlinks.

Design

The site design should be consistent in the sense that the interaction works the same on all pages.
The layout should be clean, give a professional impression.

Authority of the site and the author

The main factors that can give authority to a site:

Specialization

Must (unless it is an encyclopedia) specialize to obtain an authority that creates backlinks, and do not pose itself as a competitor to a greater number of webmasters.

Page size

It goes without saying that the larger the size of an article is important and more likely it is to get backlinks. On the other hand, short articles seem preferable for the engine.
Some sites solve the dilemma by dividing the articles into several pages. The rule of division is as follows: Each page corresponds to a query on search engines.

External Links

They enrich an article and improve its position in results and therefore the traffic, but the drawback is that they send visitors to other sites.

However, wanting to keep visitors at any price would be a mistake, it is better to get more visitors - to what external links contributes - than trying to keep a few.
So the benefits of external links outweigh the disadvantages, do not hesitate to add them because it often happens that articles that get the most backlinks themselves have many external links.

The variable quality of inbound links

According to Matt Cutts, that leads the Webspam team of Google, a quality link has the following characteristics:

Links in footer

These are links that are requested by those who provide elements of site such as templates for Wordpress for example. The author wants to have in a footer link on his site, and embeds the link in his template. Or they are links to friend sites.
These links obey to a general law, if they are not relevant, if they have nothing to do with the content of the blog, they have no value. Since October 2012, Webmaster Guidelines prohibit lots of footer links:

Links widely distributed in the footers are considered unnatural and part of a link scheme.

Reciprocal links

Google previously advised against reciprocal links. Then his record has been refined: it discourages excessive reciprocal links. But what is excessive?

If the links are not natural, and irrelevant, if you request a backlink when you make a link to a site, these interactions are considered excessive.
They are not if they are useful to visitors.

Reference: Interview with Matt Cutts by Eric Enge July 16, 2008.

In hopes of improving their position in search results, some sites set up link farms, these are satellite sites created for that purpose and containing quantities of links on their site.
They can also piggybacking collaborative sites to host these pages of links... before they are deleted by moderators.

List of links prohibited by Google

In Guidelines to Webmasters, it is confirmed certain types of links considered unnatural can penalize a site:

But these links are not a cause of penalty if they are in nofollow.

Javascript links

If they are easy to interpret - because Google can execute JavaScript code - they are taken into account as regular <a> tags and may even pass PageRank to the page that is linked. We know as this has been confirmed by Matt Cutts, the Google spokesman about referencing issues, especially the second point.

They are used to discover and to index pages by search engines. And so they are treated as HTML links and can pass PageRank. A JavaScript link is typically a link like this:

<span onClick="location.replace('http://www.scriptol.com/seo/')" />Anchor</ span>
or with an image:
<img src="image.jpg" onClick="location.replace('http://www.scriptol.com/seo/')"  />
It is then easy to interpret these links by search engines. But it is possible to write JavaScript code to make an URL invisible to search engines.

Disavowing backlinks is it a good practice?

There was a time when maximum backlinks on its site were wanted, regardless of the quality of these, but after the Penguin Update penalizing a site for an excess of bad links, the trend reversed and webmasters now want absolutely remove bad links to their site. Links are undesirable when there links from pages with objectionable content, or directories without visitors beside sites unrelated to yours, or paid links.
After Penguin thus a tool became indispensable: allowing a webmaster to delete (virtually) links to its site. It is now done, since October 17, 2012, this is part of Google Webmaster Tools.
This tool is not to be used by everyone, only those sites that were penalyzed by these bad links should use it.

If you are the webmaster of the site, you can find a partial list of inbound links through Google Webmaster Tools or with Bing Webmaster Tools. Otherwise, you can use tools in the Webmaster section.